Given:
Length of each side of the square = 12 in
Let's find the length of each side of the regular octagon.
We can see the parts of the rectangle which are not a part of the octagon for right triangles.
Since the two legs are equal, this means the triangle is a 45-45-90 degrees special right triangle.
Now, apply Pythagorean theorem:
![x^2+x^2=y^2](https://img.qammunity.org/2023/formulas/mathematics/college/kyirmy1vl9jvs4qin8v1poyrj7x5e6f1y0.png)
Also, we know the length of the two sides plus one leg of the octagon equals length of one side of the square.
Now, we have the second equation:
![x+x+y=12](https://img.qammunity.org/2023/formulas/mathematics/college/68p5etaagmxhjyndr4fj54ndptdp2hf3c3.png)
Now, let's solve both equations simultaneously:
![\begin{gathered} x^2+x^2=y^2 \\ x+x+y=12 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/ga0buauyvuuzcrgk4hn4gs5evyfbrms6cm.png)
Solving further, we have:
![\begin{gathered} 2x^2=y^2 \\ 2x+y=12 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/h4e25oyz62b4smueh0seest0rgulyfsbhw.png)
In the first equation take the square root of both sides:
![\begin{gathered} √(2x^2)=√(y^2) \\ \\ x√(2)=y \\ \\ y=x√(2) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/w5sa5cu1dcalwbv181wlkl70xwv6bl1d52.png)
Now, substitute x√2 for y in the second equation:
![\begin{gathered} 2x+y=12 \\ \\ 2x+x√(2)=12 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/j2rw99lx44j0lr48554fmjgtaqev86i36s.png)
Factor out x:
![x(2+√(2))=12](https://img.qammunity.org/2023/formulas/mathematics/college/t7ijegzu1dpvkhneuv2k7wjtlkmtbbk7rd.png)
Divide each term by (2+√2):
![\begin{gathered} (x(2+√(2)))/(2)=(12)/(2+√(2)) \\ \\ x=3.5 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/q6c1dvjxomh406rm5355l9c77vjqwik7wr.png)
Now, to find the length of reach side of the octagon, given that the length of the leg of the triangle is 3.5, apply Pythagorean theorem:
![\begin{gathered} y=√(3.5^2+3.5^2) \\ \\ y=√(12.25+12.25) \\ \\ y=√(24.50) \\ \\ y=4.9\approx5 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/dvbcg6fah7wrcyl0kp510b8uy4dtovujnq.png)
Therefore, each side of the octagon is approximately 5 in.
ANSWER:
5 in